The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Referring now to FIG. 1, a hard disk drive (HDD) 10 includes a hard disk assembly (HDA) 12 and a HDD printed circuit board (PCB) 14. The HDA 12 includes one or more circular platters 16, which have magnetic surfaces that are used to store data magnetically. Data is stored in binary form as a magnetic field of either positive or negative polarity. The platters 16 are arranged in a stack, and the stack is rotated by a spindle motor 18. At least one read/write head (hereinafter, “head”) 20 reads data from and writes data on the magnetic surfaces of the platters 16.
Each head 20 includes a write element, such as an inductor, that generates a magnetic field and a read element, such as a magneto-resistive (MR) element, that senses the magnetic field on the platters 16. The head 20 is mounted at a distal end of an actuator arm 22. An actuator, such as a voice coil motor (VCM) 24, moves the actuator arm 22 relative to the platters 16.
The HDA 12 includes a preamplifier device 26 that amplifies signals received from and sent to the head 20. When writing data, the preamplifier device 26 generates a write current that flows through the write element of the head 20. The write current is switched to produce a positive or negative magnetic field on the magnetic surfaces of the platters 16. When reading data, the magnetic fields stored on the magnetic surfaces of the platters 16 induce low-level analog signals in the read element of the head 20. The preamplifier device 26 amplifies the low-level analog signals and outputs amplified analog signals to a read/write (R/W) channel (hereinafter, “read channel”) module 28.
The HDD PCB 14 includes the read channel module 28, a hard disk controller (HDC) module 30, a processor 32, a spindle/VCM driver module 34, volatile memory 36, nonvolatile memory 38, and an input/output (I/O) interface 40. During write operations, the read channel module 28 may encode the data to increase reliability by using error-correcting codes (ECC) such as run length limited (RLL) code, Reed-Solomon code, etc. The read channel module 28 then transmits the encoded data to the preamplifier device 26. During read operations, the read channel module 28 receives analog signals from the preamplifier device 26. The read channel module 28 converts the analog signals into digital signals, which are decoded to recover the original data.
The HDC module 30 controls operation of the HDD 10. For example, the HDC module 30 generates commands that control the speed of the spindle motor 18 and the movement of the actuator arm 22. The spindle/VCM driver module 34 implements the commands and generates control signals that control the speed of the spindle motor 18 and the positioning of the actuator arm 22. Additionally, the HDC module 30 communicates with an external device (not shown), such as a host adapter within a host device, via the I/O interface 40. The HDC module 30 may receive data to be stored from the external device and may transmit retrieved data to the external device.
The processor 32 processes data, including encoding, decoding, filtering, and/or formatting. Additionally, the processor 32 processes servo or positioning information to position the heads 20 over the platters 16 during read/write operations. Servo, which is stored on the platters 16, ensures that data is written to and read from correct locations on the platters 16.
Additionally, the HDD PCB 14 includes a self-servo write (SSW) module 42. The SSW module 42 writes servo on the platters 16 using the heads 20. The SSW module 42 writes servo before user data can be stored on the HDD 10. The SSW module 42 may be implemented in the read channel module 28.
More specifically, the SSW module 42 initially writes servo spirals on the platters 16. Subsequently, based on the servo spirals, the SSW module 42 writes servo wedges before user data can be written on the platters 16. The servo wedges extend radially from an inner diameter (ID) to an outer diameter (OD) of the platters 16. The servo wedges are equally spaced from each other like spokes of a wheel. The servo wedges are interleaved with user data that is written between adjacent servo wedges.